Specimen holder for electron microscope



Nov. 16, 1965 A. c. VAN DORSTEN 3,218,457

SPECIMEN HOLDER FOR ELECTRON MICROSCOPE 4 Filed July so, 1965 INVENTOR.

ADRIANUS C. VAN DORSTEN BY Zwwe. fllwf ACE?- United States Patent 3,218,457 SPECIMEN HGLDER FOR ELECTRON MKCRGSCOPE Adrianus Cornelis van Dorsten, Emmasingel, Eindhoven,

Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed July 30, 1963, Ser. No. 298,764 Claims priority, application Netherlands, Aug. 29, 1962, 282,644 4 Claims. (Cl. 250-495) My invention relates to an electron microscope and in particular to a specimen holder for an electron microscope which can be moved in all directions at right angles to the beam of rays and, to prevent movements of the object during the investigation, can be clamped in an axial direction against a rigidly provided component part of the microscope.

Specimen holders for electron microscopes which can be rigidly held in position are disclosed, for instance, in Swiss patent specification 241,102 and German patent specification 756,834. In either case the clamping of the specimen holder is effected by means of springs. The pressure exerted by springs does not prevent the specimen from being moved sideways by means of focusing devices, but, naturally, it does hinder this movement.

It is, of course, undesirable that the specimen holder can porform a lateral movement in spite of the pressure exerted on it, so that an annoying shift of the image occurs. This drawback of the construction, in which the specimen holder is clamped by springs, can be avoided by enlarging the pressure with which the specimen holder is clamped during the investigation.

In Dutch patent specification 92,826 a specimen holder is clamped in position by controllable pneumatic or hydraulic pressure. After the investigation the pressure may be decreased or removed entirely, after which the specimen holder can easily be removed for varying the focusing of the object in the electron beam.

When gases or liquids are used as a means of exerting the required pressure, the space containing these liquids must be sealed from the ambient air. In one embodiment disclosed in Dutch patent specification 92,826, the specimen holder is constructed as a flat disc which engages a partition wall of the microscope housing. This wall comprises an annular recess which is closed by the specimen holder and which is sealed by rings clamped between the holder and the bottom of the recess in the partition. This construction has the drawback that when the pressure for clamping is removed the object stage can be lifted somewhat by the sealing rings. If the pressure is recovered, the specimen holder will be displaced in an axial direction. While it is true that the object stage is supported along its circumference in an annular groove in the wall of the housing of the microscope, the slightest play in an axial direction has the result that an accurate image no longer is obtained of the cross-sectional surface chosen. Furthermore, this may necessitate refocusing of the image with delay, as a consequence, of this investigation.

It is an object of my invention to avoid this drawback and to provide an electron microscope in which the specimen holder can be rigidly supported in position in the path of an electron beam.

A further object of my invention is to provide a speciment support for an electron microscope which after being clamped in place is not subject to lateral or axial movement.

These and further objects of the invention will appear as the specification progresses.

According to the invention, at least one body of semiconductive material is provided which engages the speci- 3,218,457 Patented Nov. 16, 1965 men holder, and the clamping of the object stage is effected by applying an electric potential between the body of semi-conductive material and the partition wall of the microscope housing which supports the object stage.

It has been known that very strong electric fields can be obtained between a metal surface and the surface of a semi-conductor if the surfaces are separated by the thickness of the extremely thin layer of air. The semiconductor which separates two metal surfaces between which an electric voltage is set up is forced against the one and against the other metal surface if the material is sufficiently conductive to produce electrical surface charges and has so high a resistance that the charge does not flow away if contact is made with a metal surface at a few points. The electrostatic forces may be transferred to one side of the semi-conductor by coating the other side with a conducting layer which is connected to a source of potential. The engaging surfaces, however, must be separated to obtain the desired pressure. It has een found quite unexpectedly, however, that even an evacuated space does not alter the exertion by electrical forces so that this principle has been successfully employed in an electron microscope, which must be evacuated, for rigidly clamping the specimen holder.

Suitable semi-conductor materials are slate, marble, agate and certain ceramic synthetic materials having a resistivity of approximately 10 ohm-cm.

The invention will be described with reference to the accompanying drawing in which the sole figure is an elevational view in section of the specimen stage of an electron microscope according to the invention.

Referring to the drawing, the magnet coils 1 and 2 energize the pole pieces 3 and 4, each provided with a channel 5 for the passage of an electron beam, provided on either side of a chamber in which a specimen to be irradiated by the electron beam is mounted. Between pole pieces 3 and 4 which are spaced from each other, a specimen holder 6 is provided. It has the shape of a flat disc with a bore 7 for the passage of an electron beam in the center opposite the channel 5 in pole pieces 3 and 4.

In this bore the specimen is mounted of which a magnified image is to be formed by means of the electron beam on a screen or a photographic plate or film not shown in the drawing. The object 8 is mounted on a thin rod 9 extending through a radial bore of the flat disc 6. A knob 10 is provided for positioning the specimen 8 in the aperture of disc 6 or removed out of the aperture and replaced by another.

If another portion of the specimen 8 is to be irradiated, the specimen is displaced and the flat disc is moved at right angles to the direction of the beam of rays. To that end disc 6 is supported by a partition 11 of the housing 13 which is supported in a groove 12. The diameter of the disc 6 is smaller than the inside diameter of the housing, so that in a plane at right angles to the axis of the beam the disc 6 is free to move laterally in all directions. The devices for sliding the flat disc are known per se and the radial rod 14 shown in the drawing is intended only to demonstrate that the disc can be moved externally of the housing of the microscope.

Since no air can penetrate into the beam channel, the sealing rings 15 and 16 are provided and do not hinder the movement of the disc 6. On either side of the chamber which contains the specimen the disc 6 comprises central recesses 17 and 18 in which the conical ends of the pole pieces 3 and 4 extend. These recesses are wider than the conical ends of the pole pieces so that the required freedom of movement of the disc is maintained.

The partition 11 is constituted of an electrically conductive non-magnetic material. The side of the wall facing the flat disc 6 serves as a supporting face and is provided with a truly smooth surface. The flat disc 6 engages this surface with the interposition of one or more blocks 19 consisting of a semi-conductive material. An annular block, for example of agate, may rigidly be connected in an annular groove 20 of the flat disc 6 with the interposition of a coating of insulating material 21. On the lower side of the disc the block projects somewhat to the exterior in which it engages the partition 11 and thus supports the flat disc 6. The disc 6 can now easily be moved up and down along the surface of the partition.

If the focusing has been determined at which the specimen has to be irradiated by the electron beam, an electric potential is applied between the body of semi-conductive material 19 and partition 11 to clamp together the disc 6 and the partition 11 of the housing of the microscope. This electric potential is applied between the housing and an electrically conductive adhering layer 22 which covers the surface of body 19 and consists, for example, of a vapor-deposited silver coating through a conductor 23 which passes (in an insulating manner) through the disc 6 and connects the conductive surface 22 to a lead-in contact 24 which is provided in an insulating manner in the wall 13 of the housing of the microscope. Outside the housing, current supply wires 25 and 26 connect the wall 13 and the lead-in contact 24 to a DC. source 27 in which one of these wires comprises a switching contact 28 with which the current circuit may be closed and opened respectively.

While I have described my invention in connection with a particular embodiment, it will be apparent that the invention is not limited to the particular specimen holder shown, but may be extended to any specimen supporting element capable of being clamped to a partition of the microscope housing.

Therefore, I do not wish to be limited to the particular construction described and desire the appended claims which define my invention to be construed as broadly as possible.

What I claim is:

1. A specimen holder for an electron microscope comprising a disc-like member movable within and supported by a wall of a housing for the microscope, said disc-like member having an aperture therein for the passage of an electron beam therethrough, means to mount a specimen in said aperture of said member, a body of semi-conductive material supported by a transverse wall in said housing and engageably contacting a portion of one surface of said member, and means to apply a potential between said body of semi-conductive material and said transverse wall for rigidly fixing the position of said member within said housing whereby said specimen is fixedly positioned in said aperture relative to said beam of electrons.

2. A specimen holder for an electron microscope comprising a disc-like conductive member movable within and supported by a wall of a housing for the microscope, said disc-like member having an aperture therein for the passage of an electron beam therethrough, means to mount a specimen in said aperture of said disc-like member, a body of semi-conductive material supported by a transverse wall in said housing and engageably contacting a portion of one surface of said disc-like member, a conductive layer on a surface of said body of semi-conductive material remote from said transverse wall, and means to apply a potential between said conductive layer on the surface of said body of semi-conductive material and said transverse wall for rigidly fixing the position of said disclike member within said housing whereby said specimen is fixedly positioned in said aperture relative to said beam of electrons.

3. A specimen holder for an electron microscope comprising a disc-like conductive member movable Within and supported by a wall of a housing for the microscope, said disc-like member having an aperture therein for the passage of an electron beam therethrough, means to mount a specimen in said aperture of said disc-like member, a body of semi-conductive material supported by a transverse wall of said housing, a conductive layer on a surface of said body of semi-conductive material remote from the transverse wall of the housing, a layer of insulating material separating said conductive layer and said disc-like member, means to apply a potential between said conductive layer on the surface of said body of semiconductive material and said transverse wall for rigidly fixing the position of said disc-like member within said housing whereby said specimen is fixed positioned in said aperture relative to said beam of electrons.

4. A specimen holder for an electron microscope comprising a disc-like conductive member movable within and supported by a wall of a housing for the microscope, said disc-like member having an aperture therein for the passage of an electron beam therethrough, a rod-like member extending through a bore in said disc-like member for mounting a specimen in said aperture of said disc-like member, a body of semi-conductive material supported by a transverse wall of said housing, a conductive layer on a surface of said body of semi-conductive material remote from the transverse wall of the housing, a layer of insulating material separating said conductive layer and said disc-like member, and means to apply a potential between said body of semi-conductive material and said transverse wall for rigidly fixing the position of said disc-like member within said housing whereby said specimen is fixedly positioned in said aperture relative tosaid beam of electrons.

References Cited by the Examiner UNITED STATES PATENTS 2,939,955 6/1960 Rommerts 250-495 2,953,970 9/1960 Maynard 88113 RALPH G. NILSON, Primary Examiner. 

1. A SPECIMEN HOLDER FOR AN ELECTRON MICROSCOPE COMPRISING A DISC-LIKE MEMBER MOVABLE WITHIN AND SUPPORTED BY A WALL OF A HOUSING FOR THE MICROSCOPE, SAID DISC-LIKE MEMBER HAVING AN APERTURE THEREIN FOR THE PASSAGE OF AN ELECTRON BEAM THERETHROUGH, MEANS TO MOUNT A SPECIMEN IN SAID APERTURE OF SAID MEMBER, A BODY OF SEMI-CONDUCTIVE MATERIAL SUPPORTED BY A TRANSVERSE WALL IN SAID HOUSING AND ENGAGEABLY CONTACTING A PORTION OF ONE SURFACE OF SAID MEMBER, AND MEANS TO APPLY A POTENTIAL BETWEEN SAID BODY OF SEMI-CONDUCTIVE MATERIAL AND SAID TRANSVERSE WALL FOR RIGIDLY FIXING THE POSITION OF SAID MEMBER WITHIN SAID HOUSING WHEREBY SAID SPECIMEN IS FIXEDLY POSITIONED IN SAID APERTURE RELATIVE TO SAID BEAM OF ELECTRONS. 